Polymerization of pyrrolidones and piperidones employing oxides of elements of group vi as chain initiators



United States Patent 3,174,951 POLYMERIZATION F PYRRULIDONES AND Pl-PERIDONES EMPLOYING 0E8 0F ELE- MENTS OF GRQUP Vi AS CHAHJ INETHATORSDavid Taber, Easton, Pat, assignor to General Aniline & FilmCorporation, New York, N.Y., a corporation of Delaware No Drawing.Original application Apr. 4, 1958, Ser. No. 726,323. Divided and thisapplication Lluly 24, 1962,

Ser. No. 217,979

the recurring unit is one which might hypothetically arise in thecondensation polymerization of 4-aminobutyric acid. However, earlyinvestigators, namely, Gabriel (Berichte 32, 1266 (1899)) and Schotten(Berichte 21, 2240 (1880)), observed that 4-aminobutyric acid andS-aminovaleric acid failed to undergo intermolecular condensation andyielded only the five and six membered lactams. The first disclosure ofsuch polyamides was that of U.S.P. 2,638,463 (W. O. Ney, W. R. Nummy andC. E. Barnes, May 12, 1953), involving the polymerization of pyrrolidonein the presence of an alkaline polymerization catalyst.

While useful polymers are obtained by the process described in the Ney,Nummy and Barnes patent, No. 2,638,- 463, considerable difficulty isencountered in obtaining these polymers in satisfactory yields; and,also, in the production of polymers having relatively high molecularWeights. Patent No. 2,739,959 of Ney and Crowther, which, in Example I,discloses that only a small yield of low molecular weight polymer may beobtained when an alkaline polymerization catalyst is employed as thesole promoter of the polymerization of pyrrolidone, discloses effectingthe alkaline polymerization of the lactams in the presence of a smallamount of an acyl compound, as an activator for the alkalinepolymerization catalyst; and preferably, carrying out the polymerizationof a lactam while dispersed in an anhydrous hydrocarbon non-solventtherefore, in order to increase the yield and molecular weight of thepolymer. The specific activators described in Patent No. 2,739,959, ashaving the property of increasing the rate of polymerization of lactamshaving and d-membered rings, are acyl pyrrolidones, acyl dipyrrolidones,organic peroxides, anhydrous lactones and alkyl esters. The Ney andCrowther patent discloses the use of these acyl compounds as activatorsfor the alkaline polymerization catalyst.

I have now found that the oxides of elements of Group VI of the periodictable are capable of acting as chain initiators in the alkalinecatalyzed polymerization of 5- and o-membered lactams, e.g., pyrrolidoneand piperidone. This particular class of oxides of Group VI elements hasthe roll of initiating chain growth. Illustrative of the oxides of GroupVI elements which I have found to be useful for this purpose are S0 S0SeO TeO CrO and M00 The general conditions and factors utilized forpolymerizing 5- and 6-membered lactams, pursuant to the presentinvention, may be those mentioned in US. Patent No. 2,739,959, exceptfor the presence of the oxide of a Group ice V and VI element describedin the foregoing, as the chain initiator for the polymerization, inplace of the activators specified in that patent. In general, the methodof effecting polymerization of 5- and 6-membered ring lactams, by theprocess of the present invention is as follows:

Initially, there is the preparation of an anhydrous solution of thealkali pyrrolidone in pyrrolidone. The alkali pyrrolidone usuallyemployed is sodio or potassio pyrrolidone, and may be obtained via thereaction of pyrrolidone with sodium and potassium metal or therespective hydroxides. In the latter case, it is essential to remove thewater formed thereby as rapidly as possible. The concentration of thealkali pyrrolidone employed in many instances may vary from 0.5 to 5.0mole percent (percentages based on pyrrolidone), and may range from 0.1to 19.0 mole percent. In series of experiments, optimum yields wereobtained with about 2.75 mole percent of alkali pyrrolidone. The role ofthe alkali pyrrolidone is that of a catalyst and serves as a source ofpyrrolidone anions.

The amount of chain initiator employed in many instances may vary from0.1 to 10.0 mole percent (percentage based on pyrrolidone). Theconcentration of chain initiator chosen will depend on the conversiondesired and the molecular Weight sought. The rate of the polymerizationwill depend, to a large extent, on the molar amount of chain initiatoremployed, with higher rates obtained by the use of greater amounts ofchain initiator. The polymerizations may be chain initiated attemperatures from 25 C. to 65 C. and are accompanied by a mildexothermic reaction.

In a bulk or mass polymerization, the addition of the chain initiator isfollowed by a thickening of the solution and gradual solidification ofthe mixture. The toughness of the cake will, obviously, depend on theextent of the conversion and will be dependent on the times involved andamounts of chain initiators used.

The polymerization employing the foregoing chain initiators may beconducted in a dispersion of pyrrolidone and the alkali pyrrolidone in anon-solvent for the pyrrolidone. Applicable non-solvents fall in theclass of saturated and olefinic aliphatic alicyclic hydrocarbons, i.e.,pentane, hexane, heptaue, cyclohexane, pentene, cyclohexene, etc. Theamount of non-solvent frequently employed is l to 3 parts of non-solventper unit weight of pyrrolidone, but is subject to wide variation. Thephysical state of the resulting polymer obtained via a dispersionpolymerization may vary from a thick curd to a fine powder, depending onconversion desired, ratio of non-solvent to monomer and type as well asrate of agitation.

For the purposes of comparison, there are given below, as Examples A andB, illustrations of the prior art polymerization of highly purifiedpyrrolidone, from the same batch and purified in the same manner as thepyrrolidone used in the examples appearing later in the specification ofthe process of the present invention.

Example A A 500 cc. glass flask was charged with 100.0 grams (1.18moles) of highly purified pyrrolidone. There was added 1.0 gram ofpotassium hydroxide flakes of 83% assay, the system immediately placedunder a reduced pressure of 10 mm. and rapidly heated to the refluxpoint of to C. The vapors were condensed in a vertical reflux condensermaintained at a jacket temperature of 75 0, thus permitting the returnof the pyrrolidone and, at the same time, effecting the removal ofwater. After one hour at the reflux point, the reaction mixture in thestill pot was cooled and the clear, colorless solution of potassiopyrrolidone in pyrrolidone allowed to stand for 24 hours at roomtemperature to the exclusion of atmospheric moisture and carbon dioxide.During the 24 hour period, the mixture became turbid and a scant amountof solid was deposited. The mixture was treated with 400 grams ofdistilled water, the solid filtered and thoroughly washed with water.The dried polymer weighed 0.6 gram, representing a conversion of 0.6%.The material was of low molecular weight, as indicated by the relativeviscosity of a 1% solution in meta cresol.

7 Example B I This example is an illustration of an alternatepolymerization of highly purified pyrrolidone, and closely followsExample 1, of US. Patent No. 2,739,959, which is also an illustration ofprior art polymerization of pyrrolidone.

A 500 cc. glass flask, equipped for vacuum distillation, was chargedwith 1200 grams of highly purified pyrrolidone. There was added 1.0 gramof potassium hydroxide flakes of 83% assay. The system was immediatelyplaced under a reduced pressure of 1.0 mm. and rapidly heated to effectthe distillation at 90 to 100 C., of 20 grams of pyrrolidone and water.The resulting clear,

colorless solution in the still pot constituted a solution of,

potassio pyrrolidone in pyrrolidone. The solution was allowed to cool toroom temperature and stand for 24 hours to the exclusion of atmosphericmoisture and carbon dioxide. During this 24 hour period the mixturebecame turbid and a scant amount of solid was deposited. The contentswere treated with 400 grams of distilled water, the solid filtered andthoroughly washed with water. The dried polymer weighed 0.5 gram,representing a conversion of 0.5%. The material was of low molecularweight as indicated by the relative viscosity of a 1% solution in metacresol.

The details of the present invention will be apparent to those skilledin the art, from the following specific examples, of preferred methodsof practicing the same:

Example I This example is illustrative .of the use of sulfurdioxide,

a Group V I oxide.

After distilling, at mm., about 20% of the monomer from a mixture of 120g. of highly purified pyrrolidone and 3.5 g. of potassium hydroxideflakes of 90% assay, there remained 101.4 g. into which, at 33, therewas bubbled sulfur dioxide obtained by adding to excess sodiumbisulfite, 8 ml. of an aqueous solution made from 2.72 ml. ofconcentrated, hydrochloric acid. After 24 hours at room temperature, theproduct, poly/pyrrolidone, was washed of impurities and dried in vacuoto give 12.9 g., or a conversion of 136% based on 94.5 g. of availablemonomer. The relative viscosity (c.:1, m-cresol) was 26.433.

Example II This experiment illustrates the chain-initiating property ofselenium dioxide.

From a mixture of 130 g. of highly purified pyrrolidone and 2.76 g. ofpotassium hydroxide flakes of 90% assay there was distilled, at 10 mm.,sufficient monomer to leave a residue of 115.6 g. To this residue therewas added, at 40, 1.31 g. of selenium dioxide and from the mixture therewas distilled, at 8 mm., a quantity of monomer such that the resultingmixture weighed 107.5. After 74 hours of reaction at room temperature,washing the product, polypyrrolidone, with methanol and water and dryingin vacuo left 9.0 g. of dry polymer of relative viscosity (c.=1,m-cresol) 2.519.

Example III This experiment is illustrative of the use of molybdenumtrioxide as a chain initiator for polypyrrolidone.

After distilling ml. at 9 mm. from a mixture of 130 g. of pyrrolidoneand 3.0 g. of potassium hydroxide flakes of 83% assay, there was left aresidue which was treated ml. of monomer was then removed bydistillation at 9.

mm. and the mixture was heated under total reflux at 128/ 10 mm. for 15minutes. The mixture which resulted weighed 110.4 g. After 72 hours ofreaction, the product, polypyrrolidone, was stirred with methanol,dilute formic acid, water and finally with methanol again, to give,after drying at 100/0.8 mm., about 19 g. of product of relativeviscosity (c: 1, m-cresol) 6.354.

Piperidone may also be polymerized by a process of the present inventionin the same manner as pyrrolidone by merely substituting piperidone forpyrrolidone in one of the foregoing examples.

While an N-pyrrolidonyl, or N-piperidonyl group appears to be the usualchain-terminating group of the polymers obtained, pursuant to thepresent invention, it will be apparent to those skilled in the art, thatthe polymer chains may be otherwise terminated, for instance, by theformation of the acids and the metaland ammonium salts thereof, as wellas esters and amides, which may arise by reaction of the active polymerintermediate with alkaline compounds, hydroxyl-containing compounds, oramines.

As samples of specific reagents, which may be employed to terminate thepolymer chains, otherwise than in a pyrrolidonyl or piperidonyl radical,may be mentioned water, sodium hydroxide, sodium methylate, methanol,ethanol, phenol, ammonio, ethylamine, aniline, diethanolamine. Reactionof the free polymer acid with alkaline agents such as metal hydroxidesand amines gives the respective salts. The various terminations proceedthrough scission of the terminal pyrrolidone ring, or one of thepolymide linkages, particularly the linkage between terminalpyrrolidonyl linkage and the carbonyl grouping linked thereto.Termination of the polymer chain by means of an ester, such as NHCH CHCH COOCH may be accomplished by treatment of the polymer intermediate,with methanol in the presence of a base.

Hydrolysis of the terminal ring may be accomplished by treating thealkaline containing white solid, obtained in the polymerization, withwater at 75-80 C. for one hour. The resulting product is terminated by aNHCH CH CH COOK group. Conversion to the free acid, and, consequently tothe other metal and ammonium salts, is accomplished by acidification andrespective action of alkalizing agents.

The products of the present invention are, as indicated, polyamides ofthe nylon-4 type from pyrrolidone, or nylon-5 from piperidone; and, assuch, are useful in the arts as in many applications of nylon. Inparticular, the products of the present invention, particularly those ofrelatively high molecular weight, e.g., products which have a relativeviscosity of about 2.5 or higher, as a 1% solution in the m-cresol, areuseful for the production of fibers for textile. and other usese.g., asinsulating blankets, etc. Fibers have been successfully produced fromproducts of the present invention, by drawing from a melt and spinningfrom solutions, such as solution in formic acid, followed by evaporationof solvent. Useful films, having a wide variety of applications, mayalso be produced from the productsof the present invention by meltextrusion, and by film-casting from solutions, such as a formic acidsolution, glycolic or lactic acid solution, followed by removal of thesolvent. Such films are useful in numerous applications, includingelectrical'applications, as an insulator; as a base for industrialtapes; as a lining material of glass replacement, and in a variety ofspecial packaging applications. The products of the present inventionmay also be used in plastic compression molding and extrusion moldingapplications, Where their crystalline nature, sharp melting point andmarked fluidity, in the molten state, results in faithful reproductionof the mold. Molded products, for use as con tainers, may be producedfrom powders obtained pursuant to the present invention; and, also, manymechanical and other engineering parts and materials, such as gears, cambearings, and similar machine components may be produced from them. Inthe electrical arts, the products of the present invention are useful asa coating on wire, etc., as an insulation, and for the production ofcertain mechanical, electrical parts, such as insulating bushings, fuseholders, and the like. The products are also of interest in the coatingarts as finishes for textiles, paper and similar fibrous materials, andfor use as special adhesives and other coatings.

It should also be understood that the products of the present inventionmay be compounded in many applications with other synthetic plasticmaterials, plasticizers and fillers. Among the plasticizers, which havebeen found to be compatible with the products of the present invention,may be mentioned, 0- and p-toluenesulfonamide, N-ethyl oandp-toluenesulfonamide, ethylene carbonate and propylene carbonate.

While the production of polymers of 2-pyrrolidone and 2-piperidone hasspecifically been described in the fore going examples it will beapparent that the process of the present invention may be employed forthe production of polymers of homologues of Z-pyrrolidone and2-piperidone which contain a lower alkyl (14 carbon atoms) substituenton the carbon atoms in the ring. Such alkyl substituted pyrrolidones andpiperidones which have been found to be most readily polymerized by theprocess of this invention are those in which certain alkyl substituentsin the 3 and 4 position such as 3-methyl-2-pyrrolidone,4-methyl-2-pyrrolidone, 4-ethyl 2 pyrrolidone,3,3-dimethyl-2-pyrrolidone, 4,4 dimethyl 2 pyrrolidone, 3-methyl-Z-piperidone, and B-ethyl-Z-piperidone. The alkyl substitutedpyrrolidones and piperidones may be represented by the general formulawherein Z represents This application is a division of applicationSerial No.

726,323, filed April 4, 1958, now abandoned.

I claim: 1. In the process of polymerizing lactalrns of the formulawherein Z represents Where n is one integer from 1 to 2 and R representsa member of the group consisting of H and lower alkyl groups of 1 to 4carbon atoms under essentially anhydrous conditions and in the presenceof a minor amount up to about 10 mole percent based on said lactam of analkali metal lactam as the polymerization catalyst; the improvementcomprising efiecting the polymerization in the presence of a minoramount up to about 10 mole percent based on said lactam of a binaryoxide of an element of Group VI and selected from the group consistingof S02, S03, S502, T602, CI'O3 and M003.

2. In the process of polymerizing pyrrolidone under essentiallyanhydrous conditions and in the presence of a minor amount up to about10 mole percent based on said pyrrolidone of an alkali metal pyrrolidoneas the polymerization catalyst; the improvement comprising eifecting thepolymerization in the presence of a minor amount up to about 10 molepercent based on said pyrrolidone of a binary oxide of an element ofGroup VI and selected from the group consisting of S0 S0 8e0 TeO CrO andM00 3. In the process of polymerizing pyrrolidone under essentiallyanhydrous conditions and in the presence of a minor amount up to about10 mole percent based on said pyrrolidone of an alkali metal pyrrolidoneas the polymerization catalyst; the improvement comprising effecting thepolymerization in the presence of a minor amount up to about 10 molepercent based on said pyrrolidone of sulfur dioxide.

4. In the process of polymerizing pyrrolidone under essentiallyanhydrous conditions and in the presence of a minor amount up to about10 mole percent based on said pyrrolidone of an alkali metal pyrrolidoneas the polymerization catalyst; the improvement comprising effecting thepolymerization in the presence of a minor amount up to about 10 molepercent based on said pyrrolidone of selenium dioxide.

5. In the process of polymerizing pyrrolidone under essentiallyanhydrous conditions and in the presence of a minor amount up to about10 mole percent based on said pyrrolidone of an alkali metal pyrrolidoneas the polymerization catalyst; the improvement comprising effecting thepolymerization in the presence of a minor amount up to about 10 molepercent based on said pyrrolidone of molybdenum trioxide.

References Cited by the Examiner Noble: Doctoral Dissertation Series,publication No. 22, 623, University of Colorado, 1956, pages 40-48.

WILLIAM H. SHORT, Primary Examiner.

J. R. LIBERMAN, Examiner.

1. IN THE PROCESS OF POLYMERIZING LACTAMS OF THE FORMULA